The invention relates to a heat exchanger for cooling a switch cabinet and to a corresponding cooling arrangement. A generic heat exchanger has a first line system for a first coolant and a second line system, separated fluidically from the first line system, for a second coolant, the first and the second line system being coupled thermally to one another for heat exchange.
A printing machine assembly cabinet which has a heat exchanger with the above-mentioned features is known from DE 200 08 411 U1. Similar heat exchangers are also described in DE 10 2007 054 724 A1, in DE 10 2008 059 023 A1, in U.S. Pat. No. 6,053,238 A and in U.S. Pat. No. 6,039,111 A.
A persistent problem in switch cabinet cooling is that the ambient temperatures of the switch cabinet over the course of the year and also the power losses and accompanying waste heat of the components accommodated in the switch cabinet may be exposed to pronounced fluctuations, while, independently of these fluctuations, the air temperature prevailing in the switch cabinet interior has to be kept below a specific value, in order to avoid the situation where the components accommodated in the switch cabinet are damaged. The cooling apparatuses used for switch cabinet cooling, whether they be passive or active apparatuses, always have, however, a narrow cooling capacity range within which they can operate in an energy-efficient way. For example, compressor-driven cooling apparatuses work in the most energy-efficient way in continuous operation. However, the maximum cooling capacity of the compressor-driven cooling circuit which can be achieved in continuous operation has to be adapted to maximum ambient temperatures and maximum power losses of the components accommodated in the switch cabinet, so that sufficient cooling can be ensured even in extreme situations. As a result of this, the compressor-driven cooling circuit always runs in on/off operation over the course of the year, with the corresponding disadvantages with regard to energy consumption. In principle, to increase the energy efficiency of the cooling apparatus, it is desirable to keep the time duration in which the compressor-driven cooling circuit is in operation as short as possible.
In order to address this problem, combined cooling apparatuses are known from the prior art, which have in addition to an active cooling circuit, such as a compressor-driven cooling circuit or a cold water set, a passive cooling circuit or a passive cooling element, for example in the form of an air/air heat exchanger. Such cooling apparatuses are also designated later on in the application as “hybrid cooling apparatuses”. Active cooling circuits have a refrigerating machine or a cold water set, introduce the cold into the system and serve, as a rule, for cooling a cooling medium. The refrigerating machine may have, for example, a compressor. The cold water set may in the simplest case have a cold water reservoir, and in this context a person skilled in the art would understand that “water” in cooling applications is not to be interpreted restrictively, but is used merely as a synonym for the coolants or refrigerants known from the prior art, generally designated as “cooling Medium”. Passive cooling circuits accordingly have no refrigerating machine or cold water source. Active cooling of a cooling medium does not take place.
These cooling apparatuses are designed in such a way that the necessary cooling of the switch cabinet interior can be provided solely in a passive way via the air/air heat exchanger over as broad an ambient temperature range of the switch cabinet as possible and for the highest possible power losses of the components accommodated in the switch cabinet, so that the active cooling circuit, that is to say, for example, the compressor-driven cooling circuit, has to be put into operation as backup only when the cooling capacity achievable with the aid of the air/air heat exchanger is not sufficient.
Due to the fact that the structural set-up of a cooling apparatus based on an air/air heat exchanger differs fundamentally from that of a cooling apparatus based on a compressor-driven cooling circuit, in the cooling apparatuses known from the prior art it has not been possible hitherto, or has been possible only at high outlay, for the cooling circuit based on the air/air heat exchanger to be operated in parallel with the compressor-driven cooling circuit. Furthermore, in the known cooling apparatuses, to change over between the cooling processes mentioned, it is always necessary for structural changes to have to be carried out inside the cooling apparatus. For example, air routing has to be adapted to the desired cooling process by altering the pivoting of flaps and the like. This requires corresponding actuating mechanisms and the use of servomotors which reduce the reliability of the system and increase its complexity. This is critical especially in light of the fact that the failure of the cooling apparatus may cause the system composed of electronic components and accommodated in the switch cabinet interior to fail or even to be destroyed.